Grinding machine



` MalCl'lZL 1931. H FORD 1,797,857

GRINDING MACHINE Filed May 28, 1929 3 Smets-sheet 1 ATTORNEY.

I@ Ng@ March 24, 1931. H, FORD 1,797,857

GRINDING MACHINE Filed May 28, 1929 5 Sheets-Sheet 2 March 24, 1931. l HFORD 1,797,857

GRINDING MACHINE Filed May 28, 1929 3 Sheets-Sheet 5 BYMUM1-` center 5Wvolv Patented Mar. 24, 1931 HENRY Form,- OFY DEARBORN, MICHIGAN',

AssIGNon To FORD MOTOR ooMPANYy-or DEARBORN, amenacen; ecoronnrion orADELAWARE GRINDENG. MACHNE Application vfiled May 28,

The objectl of my invention' is to provide a'grinding machine of simple,durable'and inexpensiveconstruction; y kStilla furtherobject of'myinvention is to provide a grinding machine Which Will :autoinaticallygrind the bore in a split type valve bushing. These valve bushingsconsi'stlofa pair of semi-circular halves -so formedl that When' placedtogether (a bushing very similar to the solid valve bushing 'ordinarilyusedfin motor car engines in produced.A f

Many'advantages are' gainedjv'hen these bushings :\1"e;'i1se"cl'y in an'engnathe. principal advantage bei ng' that each half# of: the bushingvmay be die' castjseparately andallovved to' chill'intlie `moldth'ereby`forming an eX- trennelyv hardA`V valve stem bearing. surface fortheb'us'hing.- Then'ieeting Hat-faces are then ground on an' ordinarysurface grinder! after which the outer` diameter ot a pair oflbu'shings?is ground' round.' rIfhe semi-circular bearing surfaces in whichthe"valve stemrecip'rocatcs are thengrou'nd Withr` a' large Jforni Wheehthe cutting .edge olitvhich li'a's previousbeen dressed to the'radius ofthevalve stem.

, It may be readilysee'n that these busliings were made solid 'insteadof in'halves, the

bore inthe bushing Would have to-be drilled n or ground with a Wheelo'fsmaller dia-meter than the'valve' stem.: Drilling chilledbushingsis, of'course,` impossible; Whilegrinding'lthe' bore with" a'nextremelyjsniallivvheel is not `rcomme'rc'ially` successful.l With thi-sso called i, split bushing,` the' applicant uses: a l'arge'f'orm Wheelto grind the valve stem bearing surface, and thegrindingv machine whichis the subject of this application" performs thisfgrinding operation.

Each of these half bushings must be an exa/.ct duplicate of'each other,`the bearing'surfaces must be aneXact-semicircle havinga hired radiusandA the outer" circumference must be concentricrvith the borejso thatrany tivo'ha'llivbushings which maybe picked at random Will'produce aperfect bushing.

Still a further Obj ect of myinventilon' is t-oV provide a grinding'machine in which" the Work to be ground is rotated arou'ndax'edtoposition adjacent to aser'ies'of're- 1929. serial No. aeeeec.

radial position o't/heworl-: as it'rot'ates so that th'eline 'diconta'ctofthe 'Work with the revolving' grinding Wheels isY tangent to theWheels. f

In most progressivemachine operationsthe piece to be machined ispassed"y from one machinel to the neXton' al conveyor or some siinilardevice,y the piece; being clamped tothe conveyorv or reclamped infieddies on each machine. Due to thefeitreme'-'accuracy required intliisfparticular partg it has. been found inipractical'to usean'y typeof conveyor or the 'like'sfbr' advancing the *Work yfrom onegrindingwvheel tofthe next as the location* of the Work in reference* toeachl succeeding grinding Wheel cannot be held accurately enough'.If'th'e yWorlifis successively clamped in af series of' diesf held -Vinfixedj position in relation vto the grinding:ivheelsthe variationobtained when clamping the4 Work in the various diesprbduces variationsin the 1 tinished dimensionsiofithe piece:

In the majority of grincliiigopei'ations in which great vaccuracy isobtainedhtlie Work isv 'rotated around a" center andthe grindingv Wheelmoved againstthe Work thereby grinding a very' accurate'- circumference,Qnly arcuate surfaces may begroundLby'this method-because regardlessofhoW' large the-radius of' gri'ndingis made" an' arc'l Will be' formedand not anat surface. i 1

ln' the applicantsmachine the Werl;- i`s rotated arounda' iXed'centerand the distance of the ivor'k from the fixed cent-er is varied the Workrevolves. so that the successif'e points of'contactofthe Workwith thegrinding Wheel results-inY a straightline. The accuracy obtaincdwith thecircular grinding processr isv t-hus1obtained together Withf theadvantage? thfatflativork" may be' ground thereon.

With a very:l minor changeV in the" applicants mac-hine',y.surfaces= maybef ground to a desiredfirre'gularcontour. These irregular surfacesare-very difiicult to grind'to accurate di'in'en'sionsby any* othermethod known to the'applicant. A-lth ugh the grinding ot" a piece havinga" dat surface ist Kn'iforeA` fully cleseibefd' inl the specificati"a'nyfirregular or arcuate surface may be just as readily ground in themachine.

Still a further object of my invention is to provide a novel means forrotating the Work holder very slowly while the work is being f groundand rapidly between the grinding operations. Various designs ofelliptical gears have been used to vary the velocity of two shafts, butthe limit of variation obtainable with these gears together with theVfact that smooth grinding work cannot be accomplished where this type ofgearing is used has made it imperative that a variable motion devicehaving a wide range and smoother operating characteristics be devised.The applicants structure is very simple and produces a very steadyacceleration and deceleration of the work holder.

Still a further object of my invention is to provide a grinding machinein which the work is resiliently held in a. work holder and to providemeans so that when the work holder is rotated through one revolution thework will be automatically discharged from the machine. It is onlynecessary in the applicants machine to place the bushing into theV workholder, they being automatically conveyed to each of the three grindingwheels and then automatically discharged from the machine.

With these and other objects in view my invention consists in thearrangement, construction and combination of the various parts of myimproved device, as described in the specification, claimed in theclaims, and illustrated in the accompanying drawings, in which:

Figure 1 shows a vertical central sectional view through the mainspindle of the machine. i

Figure 2 shows a sectional view taken on the line 2-2 of Figure 1. v

Figure 3 shows a diagrammatic view of the work holders, grinding wheels,and stationary cam, to illustrate the sequence of the grindingoperations and the method used to develop a fiat grinding surface.

Figure 4 shows a plan view of one oi the work holder assemblies.

Figure 5 shows a sectional view taken on the line 5-5 of Figure 4. y

Figure 6 shows an enlarged sectional view taken on the line 6 6 ofFigure 5, aud

YFigure 7 shows a sectional view of the inner side of the work holderonv the line 7 7 of VFigure 1. Y

Referring to the accompanying drawmgs.

I have used the reference numeral 10 to indicate generally the base ofthe machine. This base 10 consists of a rectangular box shapedstructurehaving aflat machined upper surface 11 to which the variousparts of the machine are secured. A'rim 12 is secured to the late 1'1and extends around its outer edge to orm a pan or trough for collectingthe meist? cooling Huid used with the machine. The base member 10 isinternally braced to give great rigidity to the parts mounted thereon tothereby secure very accurate work with the machine.

A bracket 13 is secured on one end of the base plate 10 and extendsvertically therefrom. The center portion oi this bracket is providedwith a bearing 14 for the main spindle of the machine. In this machinethree grinding wheels. are rotated by means of electric motors and thework to be ground is passed successively underneath each of thesewheels. Each of the electric motors 15 are secured to a slide 16 whichis mounted for radial movement in the bracket 13. The slides themselveshave not been shown in detail as they are of ordinary structure and)form no` part of the invent-ion except as a means for adjustablymounting the grinding wheels. y

The motors 15 extend forwardly from the slides 16 and guard members 17are secured tothe opposite side of the 'slides and partially enclose thegrinding wheels used kon the machine. The grinding wheels, motors andslides are of the conventional direct'connected type used for ordinarygrinding.

Three grinding wheels are provided, as shown in the diagrammatic view inFigure 3. The lirst and second wheels 18 are roughing wheels, while thethird wheel 19 is a finishing wheel. As the grinding wheels wear downthe slides 16 are moved inwardly to compensate for-the wear of the wheelso that the travel of the work to be ground can be a fixed path,irrespective of the wear on the wheels.

The opposite end of the base plate 10 is provided with a housingV 21which is secured tothis plate by means of an integral flange 22. Abearing 23 is formed in the outer end lof housing 21 and is aligned withthe bearing 14 in the bracket 13. Y

A spindle 24 is rotatably mounted on the bea-rings 14 and- 23 and a cap25 is secured to the outer end of the bearing 14 to absorb the endthrust produced by the spindle 24. A second cap 26 is secured Vover theouter end of the bearing` 23 to enclose the spindle 24. A thrust ,screw27 is secured in the spindle 24 adjacent to the cap 26 and a thrustplate28 is resilieutly mounted in the cap 26 by means of the springs 29 sothat the spindle 24 may be resiliently urged against the thrust plate 25by the springs 29.

. A drum shaped member 30 is formed integral with the spindle 24adjacent to the inner end of bearing 14 and extends radially therefrom.vA plurality of bearings 31 are provided in the'periphery of the drum 30parallel to the spindle 24 and a work holder assembly is rotatablymounted in each of these bearings V3l. In the vform of machine hereshown, eight work holders are provided equally spaced around the drum30. When the spindle 24`rotatcs in the bearings 14y and 23th=eY.dru1`n'30 and worlt'holders 4also rotate'.

v4Referringto FiggureV 47 a *sleeve V3Q is' rotata'# bly mounted in eachbearingl 3l, the oute'r'end of. eachI sleeve having y an' arm 33extending alngthe periphery of the drinn 30. A 'hloch 34 is formedintegral with` theouter oft-he arm 33"and is of rectangular shapeY andhas an outwardly opening .longitudinal slot 35 formed therein.l A pairoffpl'ates36 partially enclose the slot'35 andare securedI to the blockmeans of the screws 37. space, slightly wider than the thickness ofthegrinding-'wheels 18.*-0119 is allowed betweenthe two plates 36'vso thatthere is ample clearance for these wheels to operate between the twoPlatesf The inner end kof each=sleeve`32 is secured to a second arm 33by means of the screws 39 and extendssubstantially parallel to the arm33; A roller 40 is pivotally mounted between th'eears 421011 the youterend of the arn138 by nreans of a pin 41. 7 y

The construction just referred to consists briefly of a sleeve havin-gapairof arms eX- tending from' each side* nthereofgfone of` the armsbeing provided with a roller atfits outer end-and the other arm withalblock so that movement ofi'theroller willcau'se' a like move- A shaft43 `is extended through the sleeve 32 and anarm 44 is formed integralwith the outer' end of the shaft and extendssubstan- Y ,tially parallelto thearm 3,8. The outer end I the plates 36g ofthe arin44'extends intothe slot 35 in the bloclt34- and a; shoe 46 pivotallysecured totliisarmrwithin the slot 35 by means of a pin 47. The outer face of theshoe 46 is provil-led with a`v V-sha'ped groove so that the bushing tobeA groundp shown by the dotted lines 48, may be clampedv between this Vshaped groove inthe'shoe andthe plates 36. There is aconsiderablemovement of the shoe 46 within theslotv 35 sothat when the arm 44 is.rotated clockwise, referringv to Figure 5, theshoe 46 will clamp thebushing 48 against y A-lever 45 is fastened to the inner end of theshaft 43 bymeans lof the'studs 49 and eX- tends' in thegeneralYdirection of the arm 38. Aleaf spring 61` is secured to the` leverl 45adjacent to its hub` also by means offthe studs 49 and the `outer end'of this springbears againstan adjustable stopsecured to the lever 3 8.Then the spring 6l is installed it is flexed to such position Vthat 'theshaft-43 and a11n744will resilientlyV force the shoe 46 against theplates 36; VAn eccentric sleeve 5() is rotatably mounted on a. stud 62extending from the arm 3S beneath thefspring61- Suitable slots 5L areprovided in theper-iphery' of thev eccentric '50 'forrotatngsame" forady justment.; .A nutl isarranged tolo'ck'the ec- 5f() in anydesiredpesitioii around the Tt may 'thus be seenthat rotating "the'eccentric 56'w`ill vary` the spring pressnreof the leaf spring 61thereby varying,the pressure operator' of the machine is thus able toresiliently' clfampthe bushing 48 between the shoe 46 and the plates 36withjafwide range of adjustable springpressures` lWhen it is desired torelease the bushing 48 f fro'rnfbetween the plates l36and shoe 46,1 theouter e'nd ofthe leyer 45 is moved inwardly thereby rotating the shaft43r'against the5 r'e'- f silient pressure of the spring'61 ltotherebylower lthe shoe 461from ther bushing. This ysaine operation isrepeatedwhen itis desired toinsertia new bushing intheb'lock 34'.l

y It will be'noticedthat the'sle'eve32', shaft 43. arnis 33, 33,` and445 together with'tlfe lever 45 and spring 61,Aoscillate asa. unitin thebearingl during allof the;` grinding operations. The bushing 48 isVclamped at the beginning of arevolntion of the dru1n3() and is notreleased untilit'hais passed beneath the three chlferentI grindingwheels ofthe machine. y y l y A cover plate '53 is secu'redto the innerend of the'ho'usingil kand an extensionj54 is formed integra'lwith thiscoverplate 53 and extends between. the' cover plate and the M.

such position that when the drum' 30 is ro- 4.

tated the rollers 40'will follow the contour of this com 52' to therebyoscillate the lsleeves f 32 inthe bearings '31.

` Three substantiallyllat'portions 56 aregprovided on theicani 52` sothatthe'rollers 40 will operate thesefat port-ions' when the:

bushings 48 are' being.A ground by the grin`ding wheels. Tt may bei welltotinention here that due tothe "arcuate travel ofthe sleeve 32,

the cani surface 56 isnot exact-ly flat butl is .i

ofV such a contour that al straightl snrf'a'ce willl be ground bythewheels 17 and 18in the bushings 48; ln the 'building' of the inachine,vthe cani 52 is niachinedto approximate size andv thenmoun'ted on thecoverj 53.

grinding wheels' 18"; and l9`a21f1d` a: finished bushing is placedinrthe work holder.' A portable grinding wheel is rotatably mounted on A-,solid steel wheel isf clampedv in placeof the the clevison the endofthe`a`ri'n38-in placeY 5 of the 'roller 40kandthe'shaft` 24 is then ro?tated.' The bushing' 481is' held upagainfst the flat surface o'ftheaforei'nentioned steel roller and the slight radius is? ground o'n'thethe contour of the cam 56 to produce a corre- If an irregular surface isdesired to be ground, a template or finished piece is inserted insteadof the bushing 48 and the cam 56 is finished from this template. Whenthe machine is normally operated the ground surface will be identicalwith the template used to grind -the cam56.

The normal operation of the device is just the reverse of the methodused to grind the cam, that is, the roller'40 operates against spondingground surface Von the piece to be ground. Y Y

A pin 57 extends inwardly from the arm 38 and one end of a coil springI58 is hooked over this pin and the other end secured to the spindle 24so that the roller -40 may be resiliently urged against the cam 52 bymeans of this spring. y

A trip block 59 -is mounted in the interior of the extension 54 andprojects inwardly so that the outer end of the lever 45 will be forcedinwardly as 'itpasses this trip blocs. The bushing 48 which .is clampedinthe work holder at this time is thereby released and drops to thebottom of the machine.

v A second trip block 60 is Secured to the plate 11 in the path of theouter ends of the levers 45, so Vthat as each lever advances over thistrip block a new-bushing may be placed in the work holder by theoperator of the machine. Vhen the drum 30 advances so that the outer endof a lever 45 slides over the trip block 60, the spring 61 clamps thebushing 48 between the shoe-46 and the plates 36.

Means have been provided for increasing the speed of the spindle 24 whenthe bushings 48 are travelling between thefgrinding wheels. If aconstant rotation ofthe shaft 24 were provided, only a very smallpercentage of the time required for one rotation of each shaft would beutilized in grinding the bushings, and as the grindingoperation is suchthat an appreciable amount of time must be taken for grinding eachbearing, a great saving of time is obtained ifthe spindle 24 is speededup between the grindingoperations.

A sleeve 63 is rotatably lmounted on the spindle 24 adjacent to thebearing 23 and the worm wheel 64'is secured to thissleevc by means of aradial flange 65 formed integrally with the sleeve 63. A gear 66is'machined in the opposite end of the sleeve 63. A worm 67 is mountedin the lower part of the housing 21 transversely-to the spindle 24 inposition to' mesh with the worm wheel64. Y Suitable bearings 68 are'provided for this worm and anY electric motor 69 is connected theretothrough an extension shaft, notshown in the drawings- The Arotation ofthe motor 69 thereby rotates the worm 67 which operates with the wormwheel 64 to rotate the sleeve 63 and gear 66.

An arm 70 is. rotatably mounted on the spindle 24 adjacentto the` sleeve63 and extends downwardly to a position near the base plate 10. Abearing 71 is provided in the lower end of the arm 70 parallel with thespindle 24 and a shaft 72 is rotatably mounted in this bearing. A gearwheel 73 is secured to the rear end of the shaft 72 by means of kcys 74and a cap screw 75 and washer 90.

An eccentric 76 is secured to the shaft 72 adjacent to the forward endof the bearing 71 and a pinion 77 is formed integral with the forwardend of this shaft adjacent to the eccentric 7 6. The gear 73, shaft 72,eccentric 7 6, and pinion 77 are for all purposes a unit and rotatetogether at all times. A bull gear 78 is secured to the spindle 24 bymeans of keys 79 and a nut 80 in positionto mesh with the pinion 77.

A link 81 is pivotally secured to one wall of the housing 21 by means ofa pin 82 and clevis 83, the latter being formed integrally with thehousing 21. A large split bearing 84 is formed on the opposite end ofthis link which is j ournalled on the eccentric 76. This bearing isprovided with the conventional bearing cap `85 lwhich is secured theretoby kmeans of the screws 86.

When the shaft 72 is rotated, the eccentric 76 rotates with it andoscillates the link 81 around the pin 82, the link being free toosciliate in an arcuate path around the pivot pin 82. The shaft 72 beingmounted inthe bearing 7l of the arm 70 which is rotatably mounted on thespindle 24, is not free to oscillate in this arcuate plane but is onlyfree to oscillate in an arcuate plane having the spindle 24 as a center.It will thus be seen that when the shaft 72 is rotated an oscillatingmovement will be imparted to the link and arm 81 and 70 around the pivotpin 82 and spindle 24, respectively, the link 81 compensating for thevertical movement of the eccentric and the arm 70 compensating thelateral movement of this eccentric.

To operate the device, the motor 69 is started which rotates the worm67, worm wheel 64,'and gear 66. The gear 73 being in mesh with the gear66 thereby rotates the shaft 72, eccentric 76, and pinion 77 in acounterclockwise direction, referring to Figure 2. As has beenpreviously explained, the rotation of the eccentric 76 oscillates thearm 70 and shaft 72 around the Spindle 24 and, as the pinion 77 isformed integral with the shaft 72 the bull gear 78 would also beoscillated if it were not for the rotary movement imparted thereto bythe pinion 77. This gear 78 will thereby rotate in a clockwisedirection, looking from the forward end of the machine, an amount equalto the pitch line of travel of the pinion 77 plus the movement of theshaft 72 around theV center of the spindle 24. This results in a fastmovement n of the gear 78 and spindle 24.

This aforementioned movement occurs during one half of the revolution ofthe ,shaft R15-.the movement of thel arm 7() in the opposite direction.rlhis results in a slow movementl offthe spindle 24.

h vrlhe ratio of Vhe pinion rWto the bullgear '18 islas one isto eight,so that there willibe eight variable speed cycles of the bull gear 77litor veach revolution thereof.

As there -are cightwork holders on the drum 30, each cycle advances thedrum the distance between each workholder. 'The partsfoit the-device areso timed that during'the slow movement ofAv the vdrum ,30 the bushings48 in the worklliolders 34 will be passing beneath the grinding wheels18 and 19. 'Y

Any desired grinding speed canfbe obiained .for the bushings V48 vbyvarying Athe ythrow of the cccentric relative tothe pitch circle Iof the`pinion ZTQ this device one half vorthe operating cycle ot lthe machineis used to move the bushingsl between the grindn ing wheels ,whiletherest yof the cyclevis used for the actual grinding operation on thehushing. A much greater production is woby tained by the use of thisstructure over a machinein which .a constant velocity isgiven tothe drumr80. y

The lubrication of the device is accomplished by providing a pocket 87in thebase plate 10' adjacent to the gear 73 which vmay be filled withoil so that when the gear 73 rotates through this pocket the gear teethwill be lubricated. A second pocket 88 is also provided in the baseplate 10 adjacent to the eccentric 76 and is also filled with oil sothat this eccentric may be likewise lubricated. A third pocket 89 isprovided in the housing 21 adjacent to the Worm 67 and is also filledwith lubricant to lubricate the worm GT and worm wlieel64. Suitable oilcups andiittings are provided for the other bearings ot the machine butare not shown in the drawings because of their conventional nature. L'

Many advantages arise through the use ot my improved grinding machineand it may he Well to point out that with this machine a fiat straighttrough may be ground in a piece of Work which is attached to a rotatingwork holder thereby insuring .great accuracy in the ground surface.rlfhe work is not reclamped between any of the grinding operationswhich. adds materially to t-lie accuracy obtained. Y

Further, a novel means is provided for varying the speed of rotation ofthe work holders, and one which produces a .very steady acceleration anddeceleration ot this work holder.

Some changes may he made in the construction, arrangement, andcombination ci' the various parts of my improved device A the cam,

.without departing from the spirit of my ii1- Vvention fand l it; is myintention to cover by myclaimssuchV changes .as may reasonably'Ibeincluded within the scopeftliereof.

il claim as. Iny invention l. In a grinding machine, a drum-loiatmachine, an aruiextendingffrom one end, of

each of said shafts' having aroller rotatably mounted thereon inposition toco-act with the cam.,`. a second `arm"extending front theoppo- 'site enld `1 oteach of said .shafts in position adj acenttosai-d. grinding wheels, and a work ofthe path of the .work holders.-will; be tangent to each of saidv grinding wheels.

2. .Inagrindingxmachinehaving .a drum rotatablyr mounted, a sleeve`mounted in. said ndrum parallel to its axis, a ldriven grinding wheel, astationary.y cam;1nember,an armextending from Voneend. oisaid sleeve; toposition ad) acent to: the grinding-wheel andfhavying a work holder.formed, .on its .outer end,

a second arm extending from the opposite end of said sleeve to-aposition adjacent to extend-ing to .position tocofact. with said Workholder, and a. spring secui'edto the kopposite end otsai-d shaftv` and(3o-,acting with said second mentioned arml toresilieiitly vurge the jthird mentioned arm into engagementfwith sai d work holder.r

3.` vIn a grinding machine, a drumrotatably mounted, a plural-ity ,ofdriven Y grinding Awheels mounted laround said-drum, a plu- `formed onits outer end, .a second arm extending .trom 4the opupositeend `of. saidsleeve adjacent to the cani and having a roller pivotally mountedtherein, a :shaft extending through said ,n sleeve, anr arm secured to.the said. shaftand extending into the work holder and ,adapted to. clampthework to be ground insa'id work holder, a leaf springsecured tothe.opposite end orf-said shaft, andan eccentric'bushing rotatably mountedon the said second mentioned arm in position to co-'act with saidleatspring `for varying the clamping .I pressure between the third mentionedarm and the'work holder.

`In a grinding machine, a spindlerotat` ably mounted, a v.work 'holdersupported 1 by .said spindle, aigrinding wheel in -positionjsolthatiwhen said. spindleis rotatedthe `work holder willtravel.adjacentftheretm an arm rotatably mounted on said spi-ndle, ashaftL al shaft extending through `said "sleeve, a third arm secured-tosaidshaftand hold/cr. secured .-toithe. out-er end of ,eachl secondmentioned arm,1the `partsbeing so ari-anged. that as the-drumrevolves aportion rotatably mounted in said arm parallel to said spindle, meansfor driving said spindle through said shaft, and means for oscillatingsaid arm to vary the rotating speed of said 5. In a grinding machine, aspindle rotatably mounted and having a drum secured to one end thereof,a `plurality of grinding Wheels mounted on said machine, a plural- `endof said shaft and in mesh with the driven gear, an eccentric secured tosaid shaft, and

an eccentric arm rotatably mounted on said eccentric and pivotallymounted in said machine, the parts being so arranged that a uniformmotion of said driving gear will produce a non-uniform motion of saiddriven gear.

6. In a grinding machine, a plurality of grinding Wheels mounted in saidmachine, a spindle rotatably mounted in said machine, a plurality ofWork holders carried by said spindle, means for moving the Work holderstangent to said grinding wheels :over a por tion of a revolution of thespindle, and means for varying the speed of rotation of said spindle sothat the said Work holders Will travel substantially slower over thetangential path than over other portions of their travel.

7. In a grinding machine, a plurality of driven grinding Wheels, aspindle rotatably v mounted in said machine and having a drum securedVthereto, a plurality of Work holders mounted on said drum and arrangedfor tan- 'gential movement relative to said grinding wheels, a drivinggear rotatably mounted on said spindle, a driven gear secured to saidspindle, an arm rotatably mounted on said spindle between said mentionedgears, a'shaft rotatably mounted in said arm, and gears on each end ofsaid shaft in mesh with said first mentioned -gearsrespectivay, aneccentric secured to'said shaft having an eccentric arm pivotallymounted in said machine, and means for driving said driving gear.

8. In a machine ofthe character described, a frame, a tool rotatablymounted on said frame, a drum rotatably mounted on said fra-me, a Workholder pivotally mounted on a fixed aXis in said drum, means forclamping Yan article in said Work holder, the surface of said article tobe machined being spaced from said aXis, and means for oscillating saidwork holder as the drum revolves so that a nonincase? circular path isdescribed by the surface to bc machined.

9. In a machine ofthe character described, a frame, a tool rotatablymounted on said frame, a drum rotatably mounted on said frame, a Workholder pivotally mounted on a fixed axis in said drum, means forclamping an article in said Work holder, the surface of said article tobe machined being spaced from said axis, and a stationary cam aroundwhich said Work holder revolves adapted to oscillate said Work holdersso that a non-circular path is described by the surface to be machined.

10. In a machine of the character described, a frameV having Va toolrotatably mounted therein, a drum rotatably mounted in said frame, aWork holder rotatably mounted on a fixed axis in said drum and means foroscillating said Werl; holder as the drum revolves so that the resultantpath of the Work holder will be tangent to the rotatingtool.

11. In a machine of the character described, a frame having a grinningWheel rotatably mounted therein, a drum rotatably mounted in said frame,a plurality of Work holders mounted to rotate on fixed axes in saiddrum, and means for oscillating said Work holders as the drum revolvesso that the resultant paths of the Work holders Will be rtangent to thegrinding Wheel.

